Olefins have long been desired as feedstocks for the petrochemical industries. Olefins such as ethylene, propylene and the butylenes are useful in preparing a wide variety of petrochemicals, including, but not limited to, methyl tertiary butyl ether and polymers. Accordingly, a large number of processes, described in the literature, are directed to the production of olefins.
This is especially the case in recent years where there is an increasing demand for light olefinic gases with shrinking supplies of suitable feedstocks for producing such olefins. Thus, the petrochemical industry is continuously looking for processes which can provide for improved flexibility in producing various olefins from hydrocarbon feedstocks.
For example, Leyshon et al., U.S. Pat. No. 5,026,936 teaches a process for the preparation of propylene from C.sub.4 or higher feeds by a combination of cracking and metathesis wherein the higher hydrocarbon is cracked to form ethylene and propylene and at least a portion of the ethylene is metathesized to propylene. See also, Leyshon et al., U.S. Pat. No. 5,026,935.
However, despite the prior art teachings there remains a need in the art to provide a more flexible method of selectively producing higher yields of olefins from various hydrocarbon feedstocks. None of the prior art teachings suggest the integration of a deep catalytic cracking process with a steam cracking process to improve flexibility in the olefin product slate. Unexpectedly, the integration of these processes results in significantly improved flexibility in producing desired olefins. Still further unexpected benefits are obtained by processing the cracked product effluents in downstream olefins purification, disproportionation and skeletal isomerization steps.